1. Field of the Invention
The present invention relates to a technique to obtain a color image excellent in color and color evenness, more particularly to a liquid composition most suitable for ink-jet recording systems, and an ink set using such a liquid composition, a method and an ink-jet recording apparatus for forming a colored portion on a recording medium.
2. Related Background Art
The ink-jet recording method conducts recording by ejecting ink to apply the ink onto a recording medium such as paper. For example, Japanese Patent Publication Nos. 61-59911, 61-59912 and 61-59914 disclose an ink jet recording system where an ink droplet is ejected by the action of a bubble formed in the ink by applying thermal energy to the ink by using an electrothermal converter as an ejection-energy supply means. With this system, a head having high-density multi-orifice can be realized with ease, and images of high-resolution and high quality can be obtained at high speed.
In general, conventional inks for ink-jet recording contain water as a principal component, and in addition, a water-soluble solvent having a high boiling point such as glycol to prevent drying and clogging at orifices. When such an ink is used for recording on a recording medium, sometimes there arise problems such as insufficient fixation, and uneven image presumably due to the uneven distribution of a filler and/or a size on the surface of the recording medium such as paper.
Besides, image quality as high as the silver salt photographic image has recently become required for ink-jet recorded image, leading to intense technical demands for higher optical density, wider color reproduction range and more enhanced color evenness on ink-jet recorded image.
Under such circumstances, various proposals have heretofore been made to stabilize the ink-jet recording process and to enhance the quality of articles recorded by the ink-jet recording process. One of the proposals on the recording medium is to coat the surface of a base paper of the recording medium with a filler and/or a size. For example, there has been disclosed a technique to form an ink receiving layer on the base paper by applying porous fine particles that adsorb a coloring material on the base paper as a filler. Recording media produced by using these techniques are now on the market as the ink-jet coating paper etc.
The followings are some of the representative proposals on the ink-jet inks in the prior arts.
(1): Addition of a Volatile Solvent or a Penetrating Solvent to the Ink;
As means for quickening the fixing property of the ink onto a recording medium, Japanese Patent Application Laid-Open No. 55-65269 discloses addition of a compound such as a surfactant to increase the penetrability of the ink. Also, Japanese Patent Application Laid-Open No. 55-66976 disclosed the use of an ink containing mainly a volatile solvent.
(2): Mixing of an Ink and a Liquid Composition Reactive with the Ink on a Recording Medium;
In order to improve the image density, the water-fastness, and bleeding as well, there has been proposed a method where a liquid composition that can improve image quality is applied to a recording medium before or after the ink application to the recording medium for image formation. More specifically, Japanese Patent Application Laid-Open No. 63-60783 discloses a method in which a liquid composition containing a basic polymer is applied to a recording medium, and an ink containing an anionic dye is then applied thereto, thereby conducting recording. Japanese Patent Application Laid-Open No. 63-22681 discloses a recording method in which a first liquid composition containing a reactive chemical substance and a second liquid composition containing a compound reactive with the chemical substance are mixed on the recording medium. Further, Japanese Patent Application Laid-Open No. 63-299971 discloses a method in which a liquid composition containing an organic compound having two or more cationic groups per molecule is applied to the recording medium, and then recording is conducted with an ink containing an anionic dye. Japanese Patent Application Laid-Open No. 64-9279 discloses a method in which an acidic liquid composition containing succinic acid or the like is applied to a recording medium, and recording is then conducted with an ink containing an anionic dye.
Further, Japanese Patent Application Laid-Open No. 64-63185 discloses a method in which a liquid composition that can insolubilize dyestuff is applied to the recording medium prior to application of an ink. Further, Japanese Patent Application Laid-Open No. 8-224955 discloses a method in which a liquid composition containing two kinds of cationic substances having respective molecular weight distribution is used with an ink containing anionic compound. Japanese Patent Application Laid-Open No. 8-72393 discloses a method in which a liquid composition containing a cationic substance and finely ground cellulose is used together with an ink. In both publications, it is shown that the obtained image is excellent in image density, character quality, water fastness, color reproducibility and bleeding problem. Further, Japanese Patent Application Laid-Open No. 55-150396 discloses a method in which recording is conducted with a dye ink on a recording medium, and a water-fastness enhancing agent that forms a color lake with the dye is then applied to provide water-fastness to the recorded image.
(3): Mixing of an Ink and a Liquid Composition Containing Fine Particles on a Recording Medium;
Japanese Patent Application Laid-Open No. 4-259590 discloses a method where first a colorless liquid containing colorless fine inorganic particles is applied to a recording medium and then a non-aqueous recording liquid is applied. Japanese Patent Application Laid-Open No. 6-92010 discloses a method where first a solution containing fine particles or fine particles and a binder polymer is applied to a recording medium, and then applied is an ink containing a pigment, a water-soluble resin, a water-soluble solvent and water. Further, Japanese Patent Application Laid-Open No. 2000-34432 discloses a recording material comprised of an ink and a liquid composition comprised of water-insoluble fine particles, reciting that images with excellent printing quality and coloring properties are obtained regardless of the types of the paper sheets.
Inventors of the present invention have studied various ink-jet recording techniques as described above and found that these prior arts can solve respective technical problems effectively, but sometimes at the sacrifice of other ink-jet recording properties. For example, it is well known that the above-described recording medium obtained by coating the surface of the base paper of the recording medium with a filler and/or a size (hereinafter referred to as coated paper) allows formation of high-quality images.
In general, in order to obtain an image of high saturation, it is known that the coloring material should be maintained in a monomolecular film state without agglomeration on the surface of the recording medium. The porous fine particles on the coated paper have such function. However, in order to obtain images of both high density and high saturation with a given ink containing a coloring material, it is indispensable to form a thick ink-receiving layer so as to cover over the base paper using a large amount of the porous fine particles, which leads to the loss of the texture of the base paper. The present inventors considered that such a thick ink-receiving layer is required because the coloring matter is not effectively adsorbed on the porous fine particles.
Following explanation is made with a coated paper having one ink-receiving layer. FIG. 9 schematically illustrates a section of a coated paper in the vicinity of the surface thereof. In FIG. 9, reference numerals 901 and 903 indicate a base paper and an ink-receiving layer, respectively. The ink-receiving layer 903 comprises porous fine particles 905 and an adhesive (binder) 907 for immobilize particles. When an ink is applied to the ink-receiving layer 903, the ink penetrates into the voids between the porous fine particles 905 by capillarity to form ink-penetrated portions 909. As illustrated in FIG. 9, since the density of the porous fine particles in the ink-receiving layer varies locally, the mode of ink penetration by capillary phenomenon varies locally. Therefore, the coloring material cannot evenly contact with the surfaces of the porous fine particles in the course of ink penetration, so that the coloring material are not efficiently adsorbed by the porous fine particles.
Further, penetration of the ink is partially inhibited by the adhesive 907, and thus the ink-receiving layer 903 has portions into which the ink could not penetrate and which cannot contribute to coloring. For this reasons, the adsorption of coloring material in a monomolecular state by the fine particles is not efficient compared with the particle amount in the conventional coated paper. As a result, a great amount of the porous fine particles are required to provide a high-quality image, impairing the texture of the base paper.
Further, the inventors have found that although the above described technique (1) can improve the fixation properties of the ink onto a recording medium, but sometimes it may cause reduction of image density or reduction of color reproduction range which is an important factor in recording on plain paper and color image recording. Further, the inventors have found that the above described technique (2) can provide a recorded matter of a high image density as the coloring material in the ink is held on the surface of a recording medium, but sometimes sufficient color reproduction range and chroma cannot be obtained supposedly due to the agglomeration of the coloring material on the surface of the recording medium. Also, by means of the above described technique (3), the surface conditions of the recording medium is improved by applying a solution containing the fine particles, but images of the same preciseness and fine color as that formed on coated paper can not be obtained. Finally, especially regarding a non-aqueous recording ink, there are limitations on the selectivity of the coloring materials and on the methods for recording. Thus, it has a problem in degree of freedom for choice.
As mentioned above, every conventional method still has a certain problem to solve. Thus, the present inventors recognized the necessity of developing new ink-jet recording techniques in order to obtain an ink-jet recorded matter of a higher quality level than that demanded today. The present invention has been made on the basis of such recognition.
Accordingly, the present invention aims to provide a liquid composition to be employed for obtaining a high quality ink jet recorded matter having a wider color reproduction range, and color evenness, which liquid composition is excellent in long term storage stability under high or low temperature conditions, and excellent in ink-jet properties such as intermittent ejectability from the recording head and clogging resistance in the recording head.
Furthermore, this invention aims to provide a method for forming a colored portion on a recording medium, capable of forming even on a plain paper an excellent ink-jet recorded matter having wider color reproduction range, excellent color evenness, less banding in solid portion, which method is also excellent in ink-jet properties such as intermittent ejectability from the recording head and clogging resistance in the recording head.
Still further, this invention aims to provide a liquid composition that is capable of forming an excellent ink-jet recorded matter having a wider color reproduction range, excellent color evenness, well-suppressed banding in solid portion, and which liquid composition is excellent in long term storage stability under high or low temperature conditions, and excellent in ink-jet properties such as intermittent ejectability from the recording head and clogging resistance in the recording head, as well as an ink set combined with the liquid composition, and an ink-jet recording apparatus using the liquid composition.
According to one aspect of the present invention, there is provide a liquid composition for forming a colored portion on a recording medium together with an anionic or cationic water-based ink containing a coloring material, comprising a solvent, fine particles in a dispersion state, wherein the fine particles have a surface charge in a polarity opposite to the water-based ink, and the liquid composition further comprises ion whose polarity is opposite to that of the fine particles in an ionic equivalence of 0.1-40 meq/l. According to another aspect of the present invention, there is provided an ink set comprising an ink and a liquid composition respectively, the ink being an anionic or cationic water based ink, and the liquid composition comprising a solvent, fine particles in a dispersion state, wherein the fine particles have a surface charged in a polarity opposite to the water-based ink and wherein the liquid composition further comprises ion whose polarity is opposite to that of the fine particles in an ionic equivalence of 0.1-40 meq/l. According to further aspect of the present invention, there is provided a method for forming a colored portion on a recording medium, comprising the steps of:
(i) applying an ink containing a coloring material to a recording medium; and
(ii) applying a liquid composition as described above.
According to still further aspect of the present invention, there is provided an ink-jet recording apparatus comprising an ink container containing an ink comprising a coloring material, and a liquid compositioncontainer containing the liquid composition as described above, and an ink-jet head for ejecting the ink and the liquid composition respectively.
After investigation to solve the above-mentioned technical problems of the prior arts, the present inventors found out that when a liquid dispersion of fine particles that can adsorb the coloring material are used with an ink, both in a liquid state, liquidxe2x80x94liquid reaction between the coloring material in the ink and the fine particles occurs to enhance both the density and color saturation of the resulting image with high reliability, and made the present invention.
In this specification, xe2x80x9creaction between the coloring material and the fine particlesxe2x80x9d, means interactions between them including, covalent bonding, ionic bonding, physical and chemical adsorption, absorption, and adhesion. In this specification, xe2x80x9cintermittent ejectabilityxe2x80x9d means ejection stability of the first droplet ejected from the recording head after a pause of ink ejection. Thus, excellent intermittent ejectability allows longer ejection pause without impairing ejection stability, requiring less frequency of preliminary ejection or suction operation for recovery, thus contributing to throughput improvement of the recording apparatus or to reduction of running cost.